1. Field of the Invention
The present invention relates generally to apparatus and methods for characterizing physical properties of an eye and more specifically for characterizing cataracts.
2. Description of the Related Art
The term cataract refers to a reduction in transparency of the lens within the eye. Although some cataracts develop rapidly, the vast majority develop over a period of decades, becoming increasingly prevalent in older populations. Surgery to remove cataractous lenses is currently a very common operation, performed by ophthalmologists, usually as an office procedure. This procedure typically includes the replacement of the cataractous lens with a plastic one, called an intraocular lens (IOL).
For virtually all cataracts, the physical process that reduces the transparency of the lens is not one that causes light absorption and thus opacity. Rather, the transparency is reduced because the material that forms the lens changes its structure in such a way that the lens scatters light. This light scatter impairs vision because it adds a veiling glare in the retinal image, reducing the contrast of the scene viewed.
Cataract surgery is not entirely without risk, and because cataracts usually develop so slowly, the question of when it is appropriate to perform the surgery to remove them is sometimes difficult. Surprisingly, as of this writing there is no widely accepted method, either subjective or objective, for determining when surgery is appropriate. One might expect that measures of visual acuity would be appropriate, but they have been shown not to be useful for making the decision about whether or not to undergo surgery. Methods currently used to evaluate cataracts for research on their prevention utilize a mixture of objective and subjective methods, namely, photographs taken using a standard ophthalmic instrument, the xe2x80x9cslit lampxe2x80x9d, are visually compared with a set of standardized photographs to pick which standard photograph looks most like the patient""s.
Cataracts have long been observed by an optical method called retroillumination. With this method, the retina is illuminated, usually using a slit lamp, and the light reflected from the retina back-illuminates the lens in such a way that regions containing cataractous material appear darker than clear areas.
One aspect of the invention comprises a method of quantifying the extent a cataract impairs vision in an eye having a pupil, an ocular lens, and a retina. In this method a localized region of the retina is illuminated such that light is reflected from the localized region and is transmitted through the ocular lens. A portion of the reflected light is scattered by the cataract associated with the ocular lens. Light reflected from the localized region of the retina is collected, and the amount of scatter is measured so as to quantify the extent the scatter impairs vision of the eye.
In another aspect of the invention, a method of imaging cataracts in an eye having a cornea, a lens, a pupil, and a retina includes illuminating a localized region of the retina such that light is reflected from the localized region through the pupil of the eye. Light reflected from the localized region of the retina is collected with an optical element. An optical image of the eye is formed on a camera with the optical element so as to produce an electronic image of the eye. The electronic image of the eye is displayed on a monitor. The contrast of the optical image can be improved by minimizing the localized region of the retina that is illuminated.
Preferably, the electronic image is shown to the patient substantially simultaneously to the formation of the optical image on the camera. Additionally, the cataract is preferably characterized by quantifying scattering therefrom. Relative amounts of scatter can be computed for different portions of the electronic image of the eye and displayed on the monitor.
In another aspect of the invention, a method of imaging cataracts in an eye having a cornea, an ocular lens, and a retina comprises holding an assembly comprising a light source, imaging optics, and an optical detector array in place by hand a distance from the eye. A localized region of the retina is illuminated with light from the light source such that at least a portion of the light is reflected from the localized region of the retina through the ocular lens. Light reflected from the localized region of the retina is collected with an optical element. With the imaging optics, an optical image of the cataract is formed on the optical detector array so as to produce an electronic image of the cataract, and the electronic image of the cataract is displayed on a display.
Yet another aspect of the invention comprises an apparatus for imaging a cataract in an eye that includes a cornea, a pupil, a lens, and a retina. The apparatus comprises a light source, a first optical path from the light source to the eye, beam-shaping optics, imaging optics, an optical sensor, and a display. The beam-shaping optics is located in the first optical path so as to receive light emitted by the light source and direct it into the eye and onto the retina. The optical sensor is positioned in a second optical path from the eye to receive a portion of light from the light source reflected off the retina. The imaging optics is located in the second optical path at a position between the eye and the optical sensor so as to image the cataract onto the optical sensor. The display is in communication with the optical sensor to display an image of said eye. The light source is sufficiently small and the beam-shaping optics has a focal length sufficiently long such that light passing through the beam-shaping optics lens illuminates a spot on the retina between about 0.05 to 0.3 millimeters in size.
In still another aspect of the invention, an apparatus for imaging cataracts in an eye that includes a cornea, a pupil, a lens, and a retina comprises a hand-held optical assembly and a monitor. The hand-held optical assembly includes a light source, first and second lenses, a beamsplitter, and a camera. The first lens is located with respect to the light source to receive light emitted by the light source and direct it into the eye and onto the retina. The beamsplitter is inserted between the beam shaping lens and the eye such that the light passes through the beamsplitter to the eye. The camera is positioned to receive a portion of light from the light source reflected off the retina and reflected from the beamsplitter. The second lens is located at a position between the beamsplitter and the camera so as to image the eye onto the camera. The monitor is separate from and movable in relation to the optical assembly and is in communication with the camera to display an image of the eye.